Electric resistance furnace



Dec. 13, 19.27n 1,652,2@0

A. J. HANSON ELECTRIC RESISTANCE FURNCE Fiied Jan.25. 1924 Patented Dec. 13, 1927.

UNITI-:n STATES 1,652,200@ PATENT OFFICE.

AEBEBT J. HANSON, OF ARLINGTON, MASSACHUSETTS, `.ASSIGrNCR T0 AMERICAN METALLURGICAL CORPORATION, OF.BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

ELECTRIC RESISTANCE E'UIIEtllAE.`

Application med ranar'y 23, A1924.v serial No. 687,914.

This invention relates to an electric resistance furnace.

One object of the invention is to provide an electric resistance furnace, and particularly an electric resistance furnace of the t pe in which the resistor is muilied or conned in the furnace wall, of novel and improved construction and in which'the resistor is supported in a manner to enable the furnace to be operated at a high thermal eiiciency and without incurring rthe liability of, short-circuiting the resistor or burning out the same.

A further objectof the invention is to provide a novel resistor support for electric resistance furnaces.

To these ends, provision is made for operatively supporting the resistor at a plurality of points in its length by a plurality of'insulating members which are spaced apart,

' and arranged to provide between them an air space surrounding the resistor. In the preferred embodiment of the invention the resistor thussupported is confined in either the top or bottom walls of the heating chamber of the furnace, or in both, and is protected or muiied by the hearth or by the top wall of the heatingy chamber. Provision 1s also made for insulating and spacinv the resistor from the hearth or the top wa l of the heating chamberto permitthe use of ametal hearth, or a metal top `wall of the heating chamber. s

These and other features of the invention will be hereinafter described, and particularly pointed out in the claims at the end of this specification.

In the drawing illustrating the preferred embodiment of the invention,

Figure 1 is a side elevation partly in section showing the construction of the hearth of an electric resistance furnace embodying the present invention. l

Figure 2 is a perspective illustrating one of the members preferably used for supporting the resistor and spacing it from the hearth. ,A

Figures 3, 4 and 5 are sectional lansilluslratng di'erent arrangements o the resistor, and

Figure 6 is a perspective of one of the insulating resistor supports used in connection with the resistor. arrangement illustrated in Figure 5.

Considerable difficulty has been'heretofore egrperlenced in those types of electric resistance furnaces in which the resistor is muiiied in the wall of the heating chamber,

the hearth or the top wall. of the heating chamber, it is desirable to confine or Inutile the resistor in the wall of the furnace. In accordance with the present invention, the resistoris operatively supported within the wall in such manner askto avoid the diiculties heretofore experienced in burning out the resistors, and at the same time to permit the furnace to be operated at high temperature and with good thermal efficiency.

.Referring to the drawing in which for purposes of illustration, the resistor is shown as confined inthe hearth or bottom wall of the furnace, 10 represents the heating chamber of the furnace having a hearth y12 upon which the articles to be heated may be placed. The furnace may and preferably will be provided with the usual ,door 13 closing one side thereof, and which ispherein illustrated as suspended upon one end of a lever 14, `pivoted at 15 in a bracket 16 on the top of the furnacey and having the usualcounter-weight 17 for assisting in raising and lowering the door.

The hearth 12 (which preferably is removable) lis heated by a resistor 2O comprising preferably the usual ribbon resistor commonly used in yelectric resistance furnaces, and which is preferably of a general sinuous shape having bends 21', 22' at opposite sides thereofV and intermediate portions 24'con- `nectin the bends. The vresistor 2O is sup-' porte by a plurality of` individual insulating supporting members 26fwhich are spaced a art; and are arranged to cooperate with different portions offthe resistor to support the same in operative position, and to proi accumulates therebelow.

vide air spaces surrounding. the portions of the resistor between the insulating supports. As illustrated in Figures 2, 3 and 4, the insulating supporting members 26 comprise blocks ofy carborundum, orother insulating material having high thermal transmitting and radiating properties. and which are provided with open slots 28 extending downwardly through the mid-portion of the block from the upper surface thereof to near the lower surface. The resistor 2O is arranged to be supported within the slot 28 having its lower edge resting upon theI bottom of the slot and being restrained from lateral movement by the side walls of the slot. The insulating supporting members or blocks 26 act to hold the edges of the resistors away from the adjacent wall portions of thefur-` nace. This is of particular importance where the resistors are arranged beneath a hearth as when they are so located insulating dust finds its way beneath the hearth and When there is no substantial space beneath the resistors this dust soon surrounds the resistors, destroying the circulation of air therearound, whereupon`they may become overheated and burn out. Such dust may accumulate for a con.- siderable period before it interferes with\the proper functioning of the resistors which are supported elevated substantially from the base portion beneath the hearth, as in the vconstruction illustrated. r n

The insulating blocks 26 are preferably arranged in the furnace wall, so as to support the resistor at a sufficient number of different points in its length to prevent short-circuitlng of the resistor, and this result may be accomplished while at the same time preserving ample air space between .adjacent sup porting block 26 to ermit efficient and unrestricted radiation om the major portion of the resistor. The insulating blocks 26 being composed of carborundum or similar material having high thermal transmitting and radiatin propertiesz do not appreciably interfere with the radiatlon of the heat from the resistor. The heat thus radiated into the air s ace surrounding the resistor passes rapidly y conduction through the hearth 12,-which is composed of a material having good thermal transmittin properties and the necessary mechanica? strength. The hearth may be of carborundum or other similar material, ormay be of metal. With v this constructiox, it will be observed that furnace,

op ortunity is a orded the heat to efficiently ra iate from the resistor, andl at the same time, provision is made rfor ermitting the heat to be rapidly remov through the hearth 12 into the heating chamberof the thus preventing the accumulation of excess heat in the vicinity of the iresistor, and cons uently reducing to a minimum the liability o burning out the resistor.

f5, a plurality of resistor sections When a metal hearth is used` provision is made forinsulating the resistor therefrom and for maintaining the top of the resistor spaced from the hearth, and for this purpQse, insulating spacing members 30 are interposed between the resistor and hearth. The insulating spacing members 30 may and preferably will comprise blocks of carborundum or other electrical insulating material having'high thermal transmitting and radiating properties and of the 'same construction as the resistor-supporting blocks 26, and may be inverted and hung upon the resistor ribbon in the manner illustrated in Figure 2. The insulating resistor supporting blocks 26 may be affixed in the wall of the heating chamber by cement or otherwise, and as illustrated in Figures 3 and 4, the blocks 26 are located in channels 32 formed lin the brickwork, andwhich are arranged to communicate with one another to form a continuous channel way of the desired sha e to conform to the shape of the resistor. lh practice, bricks known in the trade as soaps comprising splitxbricks, 2% inches jin width, .9 inches in length and 21/2i inches in thickness, may be used in laying up the spacing partitions 34 between adjacent channels 32. With this construction a channel width of 3A of an inch is provided forv rejceiving a resistor and in which the intermediate portions 24 of each loo of the resistor are spaced three inches etween the centers, whlch provides an amount of resistor suitable for heating the hearth of an ordinary type of heat treating furnace. The hearth 12 is arranged to cover both the resistor 20 and the insulating su porting blocks 26, and is preferably removaly vsupported upon the brickwork at the front and sides of the furnace.

The modification illustrated in Figure 4 is of the same general construction as that illustrated in Figure 3, with the exception that theresistors 2O are arranged in two sections, and a` double setof channels 32 are provided for receiving the resistor sections and their supporting blocks. This arrangement of the resistor'is particularly adapted for eiciently heating relatively wide furnaces, and the double resistor arrangement is particularly suitable for connection to a two-phase power system.

In the modification illustrated in Figure are arranged side by side upon the brickwork below the hearth and are connected in series. The resistor sections are preferably supported upon insulating bars 38, preferably of carborundum'or like material having good thermal transmitting and radiating properties. The bars 38 arey provided with a plurality of slots y39 therein, in ywhich the intermediatev portions 24 of the resistor sections are laid and may be cemented to the brickwork to pre lll Lesaaoo around the major portion of the resistor to permit efficient radiation of heat therefrom and rapid passage of the heat through the hearth so as to prevent the building up of an excessive temperature in the vicinity of the resistor and consequently reducing to a minimum the liability of burning out the resistor. v

llhile the diderent features of the invention have been illustrated and described as embodied in aconstruction for heating the hearth of an electric resistance furnace, they may with advantage be used for heating the dome or top of the furnace, and if found desirable, any Wall of the heating chamber of the furnace.

Having thus described the invention, what is claimed is:

1. ln an electric resistance furnace, in combination, a chamber Wall, a ribbon resistor, insulating means for supporting the resistor upon the chamber Wall arranged to provide an air space around a substantial portion of 'the resistor, and an imperforatecovering Jfor the resistor and supporting means.

2. ln'anelectric resistance furnace, in combination, a chamber Wall, a resistor, a plurality of insulatin supporting members cooperating with di erent portions of the resistor| and spacedapart to provide an air space surroundingk the portions of the resistor between said insulating supports, and an imperforate covering for the resistor and its support.

3. lin an electric resistance furnace, in combination, a chamber vvall, a resistor, a covering member for the resistor, and means for insulating and spacing the resistor from the Wall and from said covering member including a plurality of insulating blocks having slots therein arranged above and beloWsaid resistor with the resistor received Within said slots.

4. lin an electric furnace provided with a heating chamber, a chamber Wall, a plu-r rality of relatively small insulating members.

on said Wall spaced apart a sufficient distance from one another to leave substantial air spaces therebetween, a resistor engaging said members and extending through said air spaces, and an imperforate covering for the resistor and insulating members.

5. In an electric furnace provided With. a heating chamber, a chamber insulating Wall, aI refractory imperforate heat-conducting Wall spaced from said insulating Wall, a plu-A rality of relatively small insulating members between said Walls and4 spaced apart a Suthcient distance from one another to leave substantial airv spaces therebetween, and a resistor engaging said members and extending through said air spaces, certain oitu said inemn bers insulating the heat-conducting `vvall from said resistor.A

6. In an electric resistance furnace, in combination, a chamber wall provided with a plurality' or" channels therein, a resistor ribbon, and insulating blocks positioned in said channels, each block having a slot to receive an edge of said ribbon to hold said ribbon spaced Jfrom the bases of said channels and to provide an air space surrounding the ribbon between said blocks.

7. ln an electric resistance furnace, in combination, a chamber, a chamber Wall, insulating members on said wall, a resistor supported on said insulating' members spaced substantially from said Wall, an imperitorate cover for said resistors and insulating members', said cover being spaced from. said resistor.

ln testimony whereof l have affixed my signature.

amener a: nassen.

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